1. Field of the Invention
The present invention relates to a wireless communication system and, in particular, to a network search method of a User Equipment (UE) for a wireless communication system that is capable of improving network search performance for quickly acquiring the Public Land Mobile Network (PLMN) list available in which the UE is located.
2. Description of the Related Art
In a wireless communication system, a UE typically acquires the information about a Core Network through a system information message broadcast by the network and other information required for connecting to the network.
In case when a user requests manual network selection, the UE performs a network search procedure for providing a list of Public Land Mobile Networks (PLMNs), as described hereinbelow.
If the user selects the manual network selection mode, the UE performs a power scan on the adjacent PLMNs acquired from the system information received from the network and generates the result as a scan list.
Next, the UE searches from the scan list for the PLMNs supporting the frequency bands available for the UE to acquire the information regarding the available channels. The UE generates a PLMN list based on the available channel information, and indicates the user of the PLMN list. From this PLMN list, the user can select a PLMN. The UE then connects to the PLMN selected by the user and establishes data communication in response to a user request.
In the conventional manual network selection mechanism, the UE scans for all frequency bands in order to acquire the PLMN list of the adjacent PLMNs available where the UE is located. However, it takes a great deal of time to scan for all the frequency bands, and this action also increases power consumption of the UE. A partial scan search for specific frequency bands, i.e. a frequency scan in consideration of the location area, can be used to reduce the scanning time and power consumption. In this case, however, other frequency bands sharing the location area are excluded unintentionally. A conventional network selection procedure, in which the user selects a specific network manually from the list of supportable networks (i.e. a PLMN list) is described hereinafter with reference to FIG. 1.
FIG. 1 is a flowchart illustrating a convention manual network selection method for a wireless communication system. In FIG. 1, the UE selects a network through a conventional manual network selection procedure.
Referring to FIG. 1, the UE detects a manual network selection request input by the user (101). Once a manual network selection request is detected, the UE reads the information on the PLMNs available where the UE is located (103) and performs a power scan for the available PLMNs. Next, the UE searches all the channels listed on a scan list obtained as a result of the power scan for the supportable channels where the UE is located.
In consequence, the UE creates a PLMN list as a result of the channel search and displays the PLMN list on its display screen (105). If the user selects a PLMN from the PLMN list (107), then the UE connects to the selected PLMN through a camp-on process and establishes a communication in response of a user command.
In the conventional method as described above, the UE first creates a scan list containing all the channels supported by the UE and searches all the channels of the PLMNs found in the scan list. However, since the channel search is performed to all the channels listed in the scan list, it takes a long time to receive the responses from the corresponding networks. In case that multiple networks of the same operator exists where the UE is located, the channel search is likely to be performed repeatedly for the same channel, thereby increasing the channel search time, resulting in network search delay and thus service access delay.
There is another network search method in which the UE searches a specific frequency band for available channels. This partial scan search method performs network search to a specific frequency band in consideration of the location area such that the channel search time is reduced as compared to the previously described full scan search. However, the partial scan search has a drawback in that the other frequency bands sharing the location area are excluded unintentionally.
In short, the conventional full scan search method is disadvantageous in that it takes too long to search for the available networks, and the conventional partial scan search method is likely to lose the chance for identifying other available channels.